"what I personally think is one of the things that all other movies, except Cameron's, have failed in, is the ambience/atmosphere of the first movie".
Exactly. We are operating behind the curtain now. It's not happening off somewhere in the darkness, the process is right in our face. We have humanoids interacting peacefully and openly with what should be an unseen creature of violent nature. What makes sharks so scary? The fact that any second this giant tooth-ridden maw could spring towards you from the murkiness. And you won't know it or see it until it's right on you, but you know there's a large predator out there somewhere, operating off a natural instinct...to hunt.
The thing that really struck me as a particularly interesting example in Covenant was Orams death. We knew what was going to happen to Oram, there was no surprise. It was just a dirty move by David, a humanoid creation. If Oram stumbled or fell into some dark hole on accident and you heard skittering, that's scary. The music choice was alittle...odd, and the only other being in the room when this nightmare is born is a smiling android who the Alien doesn't even care about. Where's the tension? The flash of shimmering blackness, and a rapidly fading scream as someone is dragged far off into the night, that's scary. The bloody footprint scene onboard the covenant, that kind of shot is scary. Aliens in the daylight, David feeling android love for his Xeno babies, showing the neomorph stop, think, and physically access the temple? Not so much. We see, we're involved, we're behind the scenes. There's no distance, no room to create fear. But this is the David show, he's our Alien, "A survivor, unclouded by conscience, remorse, or delusions of morality". By golly he's great at it, but it's also become such a deeply philosophical sermon on artificial intelligence and introspection regarding human mortality, that it doesn't feel anything like an Alien movie.